Warming Waters May Mean More Jellyfish

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ecoRI.org: When Jen Scranton went swimming in a protected cove at Fort Wetherill last month, she felt like she was swimming “in a giant wet ball pit.” She said she was surrounded by thousands of jellybean-sized jellyfish, and although she didn’t get stung, she did feel a bit disconcerted by the experience.

She’s not the only one. Many people throughout Rhode Island and southern New England have reported unusually large numbers of jellyfish in recent years. And while this year isn’t turning out to be a big year for jellyfish in Narragansett Bay, some scientists claim that the warming of the oceans may be creating conditions that benefit jellyfish.

Jack Costello, a biology professor at Providence College who studies jellyfish, said there is considerable debate among scientists about whether there are substantial changes in jellyfish populations worldwide.

“The popular story is that we’re changing the oceans, getting rid of the fish and causing jellyfish to multiply,” he said. “There may be some truth to that, but there is also clear evidence that some species of jellyfish aren’t doing well.”

Those jellyfish species that are struggling spend part of their life cycle on the seafloor.

The only thing scientists seem to agree on is that there is great variability in jellyfish abundance from year to year that can’t be explained. Last year jellyfish numbers boomed in Narragansett Bay. Like algae blooms, some jellyfish species explode in abundance in regular cycles, while others occasionally get blown into the bay by changing currents.

“Most of the jellies that people know about are the high-profile species, the large ones we can see easily,” Costello said. These include the common moon jelly, often seen at beaches in the summer, and the lion’s mane jelly, a large cold-water species most often seen locally in April and May. The Portuguese man o’ war, a southern species familiar to many people, is perhaps the most dangerous variety, but it very seldom shows up in Rhode Island waters.

Read more about how warming waters may lead to an increase in jellyfish in New England.